Resistance of maize (Zea mays L.) genotypes against ear rot causing pathogens in Southern and Western Ethiopia

Maize production and productivity in western and southwestern parts of Ethiopia is affected by, the potential outbreaks of major diseases such as ear rot caused by Fusarium spp., dominantly Fusarium and Gibberella ear rots. Hence, maize genotypes including (commercial hybrids, open pollinated varieties (OPVs) and elite pre commercial hybrids) collected from Ethiopia were evaluated at Bako, Jimma and Hawassa Agricultural Research Centers in 2021 and 2022 cropping seasons to assess their resistance to Gibberella ear rot (GER) and Fusarium ear rot (FER). Local isolates of F. verticillioides and F. meridionale were used and the genotypes were inoculated by introducing conidial suspensions into the silk channels of the primary ears. Twenty (20) maize genotypes were used in this study arranged in split-plot design in all the environments. Maize genotypes were randomly assigned to main plots units and fungal species to subplot units. Result showed that maize genotypes exhibited resistant (R), moderately resistant (MR), moderately susceptible (MS) and susceptible (S) reactions to the inoculation. The percentage of resistant maize genotypes ranged from 25 to 45% for GER and 15 to 25%for FER across different environments. The genotypes BH661, BHQP548, CML 395/CML 202//CML 536-#, Damot (P3506W), DK 777, and Gibe3 exhibited lesser disease severity (R or MR) in most of the environments than did the susceptible genotypes (CML 395/CML202//P3812W(F2)-24-2-2-1-1-1-B-#, BH660, and BHQPY545) across all environments. Only one hybrid (BH660) showed high susceptibility to F. verticillioides, and another (BHQPY545) displayed high susceptibility to F. meridionale at Hawassa and Jimma. From the present study, it can be concluded that, the majority of maize cultivars displayed susceptibility to ear rot caused by at least one of these Fusarium spp. in most environments. Additionally, FER severity was significantly (P < 0.001) and positively (r = 0.45) associated with GER severity, suggesting that both pathogens share the same mechanisms of disease resistance. Moreover, agronomic traits such as kernel texture (r = 0.401, 0.261), ear aspect (r = 0.024, 0.310), husk cover (r = 0.147, 0.268), date of anthesis (r = 0.149, 0.09), and date of silking (r = 0.153, 0.09) were positively and significantly (p < 0.001) associated with GER and FER severity, respectively. While ear height was significantly (p < 0.001) and negatively (r = -0.164, -0.158) associated with GER and FER severity, respectively. Thus, selecting for resistance to one fungal species would likely result in indirect selection for resistance to the other fungal species. Therefore, it is suggested that, the usage of these maize genotypes in traditional breeding programs might face challenges due to undesirable gene linkages. Hence, further research on molecular markers may be necessary to overcome these obstacles and fully leverage the potential of these genotypes in breeding programs in the country.